The present invention relates to a method for operating a wind turbine, which supplies, synchronized with a network voltage, electrical power to an electrical power supply network via a converter.
In general, the invention relates to the field for the control of a converter system of a wind turbine, in particular the control of a partial converter for a double-fed asynchronous generator. For operating the wind turbine, the control of the converter in the event of a network failure presents a special technical challenge.
A method and a device for operating an electrical machine are known from EP 1 914 877 A2. The electrical machine, which may be a wind turbine, is designed to be connected electrically with the electrical power supply network. A controller is provided for the electrical machine so that it remains connected electrically with the power supply network during and after a voltage drop for an indeterminate period of time. In particular, it is known to provide a phase locked loop, which has a phase detector and at least one proportional integral (PI) filter, in the event of a drop in voltage to almost zero volts, zero voltage ride through (ZVRT). It is further provided that the parameters of the PI filter can be selected discretely depending on states defined depending on the network voltage, wherein a state machine can be accessed for this.
It is known from U.S. Pat. No. 6,941,113 B2 to control a wind turbine with a double-fed asynchronous generator via a phase locked loop. In the event of certain events in the network and/or in the wind turbine, it can happen that the phase locked loop is temporarily not synchronous with the network voltage. The phase locked loop in this case permits the wind turbine to ride through the event and only supply power again at a later point in time synchronously with the network voltage. So that the phase locked loop can be synchronized again quickly, a phase angle deviation is determined and a scaling factor is calculated from it when a minimum value is exceeded, which is applied to the setpoint values of the currents to be supplied.
The object of the invention is to provide a method for operating a wind turbine, which permits with simple means even in the case of transient voltage errors in the electrical power supply network a reliable and dynamic tracking of the phase angle and thereby avoids erratic behavior. Furthermore, a method should be specified that permits stable operation of the wind turbine over the entire voltage range.